Identification and Determination by Fast Atom Bombardment Mass Spectrometry of the Compatible Solute Choline-O-sulfate in Limonium Species and Other Halophytes

Abstract

A sensitive and specific method was developed for determining choline-O-sulfate by fast atom bombardment mass spectrometry, using a deuterium labelled choline-O-sulfate internal standard. This method was used to survey leaves or shoots of 30 native halophytic species from 14 families, collected from temperate and subtropical saline habitats. Twenty-three species had very little choline-O-sulfate (-1 dry wt) but Avicennia germinans contained 8 μmol g-1 dry wt, and all six members of the family Plumbaginaceae surveyed (Limonium spp. and Armeria maritima) accumulated > 100 μmol g-1 dry wt. Three cultivated Limonium species were also found to accumulate choline-O-sulfate when salinised with NaCl or with NaCl plus Na2SO4 under controlled environmental conditions. The identity of choline-O-sulfate in Limonium species was confirmed by high resolution and tandem mass spectrometry, by 1H nuclear magnetic resonance, and by analysis of hydrolysis products. Tests with Limonium leaf disks showed that the salt glands of this genus secrete very little sulfate. Possible roles for choline-O-sulfate in osmotic adjustment and sulfate detoxification are discussed.